It is hard to say about the P/K booster because you don't list what else you are using. Assuming your are using "proper" nutrients for the flowering stage, I would suggest that a P/K booster is just that, a booster. Most any decent "flower" nutrients should have adequate P/K levels for optimal flower growth, however I am of the opinion that a P/K booster can not really hurt if not over done, so my method is to only use P/K booster about every 7- 14 days or so, after about 2-3 weeks of flower development has occurred. This way there is less risk with overdosing and I believe that 2-3 "boosts" of P and K are all that are required during the entire flowering stage.
Concerning your worries of slow growth recently, I have a one word answer to this happening - defoliation! Every healthy green leaf you removed has reduced your plants capacity to produce energy. Fewer healthy green leaves = less photosynthesis = less energy produced = slower growth. It is that simple. De-leafing so "bud sites" grow more is a foolish concept that should have died out with the dinosaurs. Those "bud sites" are relying on those very leaves to produce the energy for those "bud sites" to grow! No leaf - slower growth. In future, try only removing yellow leaves, for by the time they are yellow, they have served their purpose. In over 35 years of cultivating cannabis, I have never come across a cannabis plant that gets rid of its own healthy green leaves. Yellow ones yes, but green ones never. Your plant needs every green leaf to be producing energy so she can grow her biggest and best flowers. Removing healthy green leaves for no apparent reason is detrimental to your plants overall well being. All you can do now is be patient while your plant struggles on with less energy. She will still grow and mature her flowers well enough, but nowhere as quickly as had you left her healthy green leaves on to produce maximum energy for maximum growth. Next time you grow, try leaving the leaves and you may be surprised how much quicker she will grow and flower. If you are keen, have a look at some of my diaries to see plants that have never had any healthy green leaves removed and to see how their "bud sites" coped with those nasty shade leaves in place. I do however agree with "lollipopping", but that is another story for another day!
Congratulations on embarking on this fascinating journey of cannabis cultivation, you will never stop learning! And the best part is.... nothing tastes as nice as home grown herbs!!
Hope this helps, and sorry for the "sermon" about de-leafing, I just hate it. ... Organoman